1. Field of the Invention
The present invention relates generally to single-handed syringe.
2. Description of the Prior Art
Syringes are an essential element in the day-to-day practice of medicine and nursing, but are also essential in industry, laboratory science, research, and animal husbandry. Syringes are used to inject medications, aspirate body fluids, provide vacuum, and transfer fluids. The syringe design most commonly used in medicine consists of a barrel made of plastic and an internal plunger which is moved into or out of the barrel, resulting in pressure or a vacuum, respectively. The difference in pressure between the volume in the syringe and the outside environment is produced by movement of the plunger, resulting in movement of fluid into (aspiration) or out (injection) of the syringe. This difference in pressure creates the desired effect of a syringe, that is, aspiration or injection.
Injection with a standard syringe is simple, and uses powerful flexor muscles of the hand and forearm. Injection with a standard syringe can usually be easily accomplished with one hand, freeing up the other hand for other necessary tasks or procedures. In this technique the 2nd (index) and 3rd fingers (middle finger) are placed on a finger flange of the syringe and the thumb is placed on a thumb rest of the plunger. The digits are brought together resulting in a powerful injection due to contraction of powerful flexor muscles of the hand and forearm. The ability to use a syringe with one hand and use the other hand for other tasks is important in many complicated procedures.
Aspiration with a standard syringe usually requires the use of two hands in order to generate the necessary power and maintain fine control. Generally, this is done by using one hand to control the barrel and the other hand to pull on the thumb rest of the plunger. The two-handed technique uses muscular strength of both the hands and the arm. Thus, very powerful vacuums with rapid movement of fluid into the syringe can be obtained. This is currently the technique of choice when either fine control of the syringe is required or considerable power is necessary. This is also the technique used by most physicians and nurses.
Single-handed aspiration with a standard syringe is possible, but is difficult and awkward. Generally, two techniques may be used. In the first method, the thumb rest of the plunger is grasped by the 2nd and 3rd digits (index finger and middle finger) and the thumb is placed on the finger flange of the syringe. The fingers are forcefully flexed, while the thumb remains extended. This results in the plunger being pulled out, resulting in an effective aspiration. There are several problems with this method including: 1) fine control of the syringe is effectively lost (which is important when there is a sharp needle in delicate living tissues); 2) the entire syringe tends to rotate, further degrading control; 3) due to the size of the syringe components relative to the dimensions and strength of the human hand this method is extremely difficult with syringes larger than 10 cc (i.e. 20 cc or 60 cc); and 4) the force of aspiration is generated by weak intrinsic flexors of the hand, without using powerful flexors of the thumb and forearm, resulting in a weaker aspiration. Thus, this single-handed method is unsatisfactory.
Single-handed aspiration may also be accomplished by an alternative thumb method. In this method, the syringe barrel is grasped by the four fingers, and the thumb is placed under the thumb rest of the plunger. With the syringe firmly grasped by the digits the thumb is extended, resulting in aspiration. Unfortunately, variations of this method are best demonstrated by drug addicts who inject themselves with drugs. The alternative thumb method has several disadvantages: 1) although a degree of control is maintained, it is not the fine control of the fingers, but the more coarse control of the forearm musculature; 2) power of the aspiration is weak, because it is accomplished by the extensors of the thumb; 3) full aspiration is difficult to achieve without changing the handgrip; 4) the syringe is generally pointing toward an operator which is the opposite direction required in a medical procedure (except for a person injecting themselves with drugs); and 5) when the thumb is extended the hypothenar tissues are compressed under the syringe, resulting in an unpredictable deviation of the needle side of the syringe with some loss of control.
Single-handed aspiration with a standard syringe is difficult and awkward, resulting in loss of fine control and power during aspiration. With loss of control, there is a higher rate of procedure failure and contamination. With loss of power, speed of aspiration is impaired, especially for viscous fluids. Because of the loss of strength and control with single-handed aspiration, procedures that demand either fine control of the syringe during aspiration or the generation of a powerful vacuum, are difficult if not impossible to accomplish with a conventional single-handed syringe.
Various attempts have been made to design a syringe which will allow for easier single-handed aspiration. Several of these designs have involved the use of a an external apparatus which is integral with the syringe and allows the plunger to be advanced or retracted using squeezing motions of digits on one hand rather than pulling motion using two hands, see for example U.S. Pat. No. 3,990,446; to Taylor et al. Other patents, such as U.S. Pat. No. 5,582,295; to Haber et al., have described essentially the same device, and some patents have described an adapter which can be fitted on a conventional syringe, see U.S. Pat. No. 5,135,511; to Houghton.
Several U.S. patents have described a syringe with an external slide which attaches to the plunger, permitting single-handed operation, see U.S. Pat. No. 4,484,915; to Tartaglia and U.S. Pat. No. 4,639,248; to Schweblin.
However, in all of the above-described designs, the position of the index and middle fingers as well as the thumb, must be moved on the syringes when switching from aspiration to injection mode, resulting in intraoperative instability. In addition, during single-handed aspiration using these devices, the barrel and needle advance beyond the index and ring finger, an unstable situation, creating major difficulties in control and localization of the needle and resulting in instability and unpredictability during procedures.